ive had that happen twice now. Once when I closed the damper to quickly, and second I went out and tapped my chim w/ claw hammer and must have been cresote in there from me burning wood, when it started falling inside the chim, I heard a big POOF and the wife started yelling

After getting a good coal fire going find some hardwood logs equal to the length of your box and place them on both sides of the box. Load up the middle with a lot of bit. Once that has caught and the blue ladies are dancing throw a few junk rotten pieces of wood where you can. This method has given me close to a 15 hr burn at times. The burnt out wood makes it easy to throw in some new bit and get it going again. Upon waking up and getting the fire active just repeat for the same results. Simple.